In a co-pending application of A. A. Wolsky, R. B. Papp and J. G. Victor 82,833 filed simultaneously herewith and entitled REMOVAL OF SOLUBLE TELLURIUM COMPOUNDS FROM A CRUDE GLYCOL ESTER SOLUTION, there is disclosed a method for the removal of soluble tellurium compounds from vicinal glycol ester solutions which were prepared by the tellurium-halide ion catalyzed liquid phase oxidation of an olefin and an aliphatic monocarboxylic acid, by diluting the tellurium-containing reaction product (oxidate) solution with at least 50 per cent by weight water and contacting the dilute water-tellurium-containing oxidate solution with a strongly acidic sulfonated ion exchange resin to retain and remove the tellurium compounds from the oxidate solution.
The present invention is directed to an effective method of recovering the tellurium compounds which have been retained on the strongly acidic sulfonated ion exchange resins as a result of the process disclosed in the described co-pending application, by eluting the ion exchange resin with a dilute mineral acid and treating the resulting tellurium-containing acid eluate to recover the tellurium in a form suitable for reuse.
To place this invention in its proper context, the oxidation reaction employing the tellurium-halide ion catalyst as well as the removal of the soluble tellurium compounds from the resulting reaction product glycol ester (oxidate) solution as set forth in the co-pending application of A. A. Wolsky, R. B. Papp and J. G. Victor filed simultaneously herewith will be described and the interrelation between such processes and the process of this invention will be pointed out.
In the U.S. Pat. Nos. 3,479,395, 3,637,515, 3,668,239, 3,689,535, 3,715,388, 3,715,389, 3,743,672, 3,789,065, 3,907,874, 3,985,795, 4,045,477 and 4,073,876 there is disclosed processes for the preparation of vicinal glycol esters by the liquid phase oxidation of an olefin, such as ethylene or propylene in a carboxylic acid medium, such as acetic acid using a tellurium catalyst and a source of halide ions.
The present invention is directed to an effective method of recovering the tellurium retained on a strongly acidic sulfonated ion exchange resin which was employed to remove the soluble tellurium from crude vicinal glycol ester solutions produced, for example, by such above described processes and containing tellurium in the form of soluble inorganic tellurium compounds and soluble organo-tellurium compounds. Because of the high reactivity of tellurium, in combination with a halide source when used as a catalyst as in the above reaction its combination with organic compounds such as the carboxylic acids and olefins employed very frequently results in the formation of organo-tellurium compounds, such as tetra and divalent alkyl tellurium halides, tellurium carboxylate compounds and the compounds described for examples in an article by Jan Bergman, Kemisk Tedskrift, Vol. 88 (11) pp. 62-3, 1976 Sweden, entitled New Production Process for Ethylene Glycol as well as other soluble tellurium compounds which remain in solution with the glycol ester reaction product. In such reaction, a portion of the tellurium catalyst such as tellurium dioxide, etc. is itself or in combination with the halide source, converted to one or more organo-tellurium compounds. The type and number of organo-tellurium compounds which may be formed and which may be recovered is a function of the reaction conditions to produce the vicinal glycol ester such as time, temperature, carboxylic acid and any solvent which might be employed. In addition, at least some of the inorganic tellurium compounds used as catalysts or formed in the reaction, such as tellurium tetrabromide, may also remain in solution with the glycol ester product.
Because of the cost and toxicity of tellurium, it is essential that as much of the tellurium as is possible be removed from the glycol ester reaction product by the ion exchange resin and the retained inorganic or organo-tellurium compounds recovered from the ion exchange resin and converted to a form suitable for reuse as a catalyst in the oxidation reaction.
There is no known prior art which describes the removal of soluble inorganic or organo-tellurium compounds from a crude vicinal glycol ester reaction product, prepared by the tellurium catalyzed acetoxylation of olefins, by treating a water diluted solution of the glycol ester reaction product with a strongly acidic sulfonated ion exchange resin or the recovery of the tellurium from said resin by eluting the resin with a dilute mineral acid forming an eluate which may be treated to convert the tellurium to a reusable form.